[Bug] Enabling accessibility feature (example talkback) causes app to crash on loading tabs tray

[abhijitvalluri]

Steps to reproduce

1. Enable TalkBack accessibility feature in Android settings.
2. Open firefox app.
3. Open the tabs tray by clicking on the tab count on the URL bar
4. App crashes!

Expected behavior

I expect the app to not crash when accessibility features are enabled and you use the tabs tray in the app.

Actual behavior

The app crashes when the tabs tray is opened with the accessibilty feature, such as TalkBack, enabled.
It appears that the culprit for this crash is this chunk of code: https://github.com/mozilla-mobile/fenix/blob/master/app/src/main/java/org/mozilla/fenix/tabtray/TabTrayView.kt#L188

if (hasAccessibilityEnabled) {
    tabsAdapter.notifyDataSetChanged()
}

Somehow when notifyDataSetChanged() is called, I get an IndexOutOfBounds exception. When I remove that code, there is no crash. I am not sure what accessibility feature notify data set changed method call provides.

The following is the error:

2020-08-31 17:50:34.173 28972-28972/network.novak.fenix.debug E/AndroidRuntime: FATAL EXCEPTION: main
    Process: network.novak.fenix.debug, PID: 28972
    java.lang.IndexOutOfBoundsException: Index: 3, Size: 3
        at java.util.ArrayList.get(ArrayList.java:437)
        at mozilla.components.browser.tabstray.TabsAdapter.onBindViewHolder(TabsAdapter.kt:52)
        at org.mozilla.fenix.tabtray.FenixTabsAdapter.onBindViewHolder(FenixTabsAdapter.kt:67)
        at org.mozilla.fenix.tabtray.FenixTabsAdapter.onBindViewHolder(FenixTabsAdapter.kt:59)
        at org.mozilla.fenix.tabtray.FenixTabsAdapter.onBindViewHolder(FenixTabsAdapter.kt:22)
        at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7308)
... (truncated)

Device information

• Android device: Android 10, Pixel 2
• Fenix version: Issue still exists on latest Firefox production and latest Firefox Nightly (Nightly 200831 06:01 (Build #2015761139)) and also on latest master (commit 4a00131)

┆Issue is synchronized with this Jira Task

[liuche]

Could you take a look at this @mcarare? I'm wondering if this is some fallout from the a11y changes we were making - I was also seeing these show up in the Google Play pre-launch report https://sentry.prod.mozaws.net/operations/fenix-fennec/?query=is%3Aunresolved+sealed

[abhijitvalluri]

As per this webpage on Android Developers Documentation: https://developer.android.com/reference/androidx/recyclerview/widget/ConcatAdapter

When an added adapter calls one of the notify methods, ConcatAdapter properly offsets values before reporting it back to the RecyclerView. If an adapter calls RecyclerView.Adapter.notifyDataSetChanged(), ConcatAdapter also calls RecyclerView.Adapter.notifyDataSetChanged() as calling RecyclerView.Adapter.notifyItemRangeChanged(int, int) will confuse the RecyclerView. You are highly encouraged to to use SortedList or ListAdapter to avoid calling RecyclerView.Adapter.notifyDataSetChanged().

So, it looks like calling notifyDataSetChanged is not a good idea with ConcatAdapter perhaps. For some reason doing this is causing a call in FenixTabAdapter's onBindViewHolder with a position value that is more than the number of tabs. What I am noticing is that it is calling this method with a position value that is upto 2 times the number of tabs available. So, if I have 3 tabs open, then this method is called with position = 0 to 5, and if I have 2 tabs open, position is 0 to 3 and so on. Hope that helps.

[mcarare]

I will take a look at this. It was working just fine , but there were a great deal of changes in Tab Tray since I have implemented the fix for this: #11542.
Including adding the ConcatAdapter. According to documentation, using this adapter breaks a11y functionality:

CollectionInfo and CollectionItemInfo will no longer be populated by default.

The question is if we want to populate this info manually or completely remove code. It will mean screen readers will never announce tab position in list .

[Diana-Rus]

Hi, I can reproduce the issue on Nightly 9/1 with:

• Google Pixel 3XL (Android 9)
  Crash link - with only one tab opened: https://crash-stats.mozilla.org/report/index/bp-574f4226-ea0e-4a90-8be3-d0aba0200901
• Samsung Galaxy S9 (Android 8)
  Crash link - with only one tab opened: https://crash-stats.mozilla.org/report/index/54eff846-45a2-4ea3-9014-420020200901

Note:

• Didn't encounter the issue when there was no tab in tabs tray
• I've encounter the issue by having at least one tab opened in tabs tray and than following the STR.
• It can be encountered as well when you follow the STR, with an extra step, after step2 you add a tab and then continue with step 3:
  STR

1. Enable TalkBack accessibility feature in Android settings.
2. Open firefox app.
3. Make a search after a site.
4. Open the tabs tray by clicking on the tab count on the URL bar
   Actual Result: App crashes!

Check GIF

Removing QA-needed until issue is fixed.

[sflorean]

Verified as fixed on Nightly 9/10 with the following devices:

• Samsung Galaxy Note 10 (Android 10)
• Google Pixel 3 (Android 11)

Note: I was able to reproduce the crash on Beta and Release.